Polymer-based electroluminescent devices PLEDs) have the potential for providing inexpensive alternatives to alphanumeric displays and x-y addressable displays. PLEDs also have the potential to provide an alternative to back lighted liquid crystal displays. A simple PLED may be constructed from an electroluminescent layer sandwiched between an electron injection electrode and a hole injection electrode. More complicated devices utilize electron and hole transport layers between the above mentioned electrodes and the electroluminescent layer. Devices based on poly(p-phenylenevinylene) (PPV), or derivatives thereof, have been demonstrated with sufficient quantum yields to be commercially attractive.
A display based on PLEDs is typically constructed by spin casting one or more polymer layers on an electrode structure. An electron transport layer and the second electrode are then deposited on the PPV layer. Individually addressable devices are obtained by patterning the electrodes and electron transport layers. All of the devices typically share a common PPV layer.
While this mode of fabrication is useful in generating devices which all emit at the same wavelength, it is less than ideal for devices in which the PLEDs are to emit at different wavelengths. For example, color displays may be constructed by constructing each pixel from three color pixels placed close to one another. To obtain pixels with different colors, prior art devices utilize an electroluminescent layer that has been doped to produce a broad emission spectrum. Color filters are then used to convert this one color display into a tri-color display. While a multi-color display can be fabricated in this manner, only a fraction of the available light can be realized at each color; hence, the intensity is less than that achievable with a monochrome display. In addition, the color filters must be fabricated and patterned on each element which increases the cost of the display.
It would be advantageous to be able to pattern PPV layers photolithographically. PLEDs could then be constructed using the well developed techniques utilized in the manufacture of integrated circuits.
Broadly, it is the object of the present invention to provide an improved PLED.
It is a further object of the present invention to provide a photolithographic method for patterning PLEDs.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.